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What The Fish? Episode 5: Shark Week 2012

The allure of sharks

Sharks, and cartilaginous fishes in general, have long mesmerized scientists and the public alike. They are fascinating creatures! Fossil remains indicate that sharks have been evolving on this planet for well over 400 million years. They have been described in popular culture as "perfect killing machines," and it is hard to argue with their abilities to hunt and secure prey of all shapes and sizes. Be it the incredible filter-feeding of the immense Whale and Basking sharks or the pure power and incredible bite of the Great White Shark, few organisms in nature portray an aura of such efficiency. Sharks are among the earliest known jawed-vertebrate lineages, and since their initial evolution, they have wasted no time in putting those jaws to work. After 400 million years they still remain some of the oceans most incredible predators with no signs of slowing down.

Sharks are Venomous and Bioluminescent?

However, there are more to sharks then just teeth! A number of lineages have independently evolved venom, including the horn sharks and angel sharks. The horn sharks release venom out of spines that stick out from each of their dorsal fins, making them an unattractive meal for even larger predatory fishes. The spines of the dorsal fins in some squaliform (or dogfish sharks) are also known to be venomous, including species within the lanternsharks. Sharks have also independently evolved bioluminescence, the ability to generate and emit light, as they have invaded the deep sea. These include predominantly deep-sea taxa, such as the lanternsharks and the bizarre Cookie Cutter Shark that sucks on to prey and rips off hunks of flesh before speeding away. These deep-sea sharks all use bioluminescence to hide from potential prey items, to avoid being eaten themselves, and for communication.

The splendid lanternshark (Etmopterus splendidus) belongs to the family Etmopteridae, the lanternsharks, in the order Squaliformes. Squaliform sharks include nearly 100 species that are found worldwide, have 5 gill slits, two dorsal fins (with venomous spines), and no anal fin. Lanternsharks are predominantly found in the deep-sea with bodies that are covered with bioluminescent photophores on the belly and sides of the shark. The bioluminescent light on the underside of these sharks are used for counter-illumination. That means the shark produces light at the same wavelength as the light that filters down below into the water column to become invisible to both prey and potential predators. Lanternsharks are small, and they rarely reach a size greater than three feet. Most species are well under a foot, hardly the dastardly animals that we think of...